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JOURNAL OF THE PLYMOUTH INSTITUTION. 

The above figure represents the larva of Boarmia repundata 
covering the cocoons formed by the larvee of Microgaster flavipes, 
from which seventy flies were bred. 
The larvee of these Microgasters when full-fed (then within the 
body of their victim) emerge simultaneously from both sides of 
the body of the caterpillar, each making an aperture for its exit. 
They then at once unite in making a web over and around the 
twig, the foundation from which the honeycomb-like mass is sus- 
pended. ‘This spinning and weaving is, to all external appearance, 
completed in about seven hours, but to finish the internal lining 
of each cell would take some time longer. 
Before and during the escape of the parasitic larve the victim 
remains on the upper side of the twig; in about twelve hours it 
will be found to have glided to the under side, and to cover the 
Microgaster cocoons containing the larve that had emerged from 
it, in such a way as to suggest the idea of affording them protection, 
as shown in the illustration. Why this marvellous proceeding I 
cannot conjecture, seeing that the unfortunate caterpillar must be 
half-dead, having had its sides pierced with seventy holes by the 
escape of these parasitic larve, and quite dead long before the 
flies emerge. 
In September last I saw the similar batch of cocoons at Laira, 
on jessamine, referred to above, which produced the extraordinary 
number of one hundred and thirty-three flies of Microgaster 
alvearius, these were from a larva of Boarmia gemmaria (= rhom- 
boidaria). 
Similar cocoons are made by Apanteles fraternus out of Aspilates 
ochrearta (=citraria); and Microgaster minutus from Cleora 
glabraria. 
The mass of cocoons in the engraving is shown after the escape 
of the fly. The majority appear to have escaped on one side, a 
few on the other. It was engraved from a photograph by the 
writer. 
SToNEHOUSE, 30th March, 1886. 
